Eurorack DIY parts

This information is for doing DIY, re-paneling, and/or repairs on Euro systems. It's not comprehensive, everyone has preferences, but lists the common, major or most-wanted parts in the Eurorack format, and/or what sort of things will work.

Front panels

Specifications

The Eurorack format was developed in parallel by Analogue Systems and Doepfer, with different approaches to module power connectors and front panel mounting holes. These days the Doepfer standard predominates.[1][2] The format is based on DIN 41494 Eurocard standard.[3]

Panels

Doepfer specifies the Eurorack front panel material as 2 mm anodized aluminium.[4] In practice panels from other manufacturers may slightly differ, e.g. Synthwerks use the closest gauge that Metalphoto offer which is 0.0625" (1.59 mm). Also check data sheets for front panel parts, e.g. the maximum recommended thickness for 3.5 mm Cliff 1384 jacks is 2.5 mm.[5]
Front panel dimensions in the the Eurorack format are specified in U and HP not in inches or millimeters. One U (unit) or in German HE (höhen einheit) is 1.75 inches equivalent to 44.45 mm. The panels height is 3U (3x1.75"=5.25" or 133.35 mm) less any allowance for mounting rail flange. Width is measured in HP (horizontal pitch) or in German TE (teilungs einheiten); 1 HP is 5.08 mm, 1/5", 0.2" or 200mil. The actual width of a front panel is a few tenth of a mm less than whatever multiple of 5.08 mm it is, to give some tolerance for final assembly. A 19-inch rack has a usable width of 84 HP.[3][4][6][7][8]

These don't include a tolerances for the screw hole in the panel nor for the nut in the rail moving up and down. It's better to give a little more clearance than suggested by these figures.[9]

Panel mounting holes

If the Doepfer specification is followed, or rails with sliding nuts are used, elongated holes are not required. These are useful for non-standard panel widths like the Piston Honda's and to compensate for for manufacturing tolerances of the panel width or hole position. They help to fit the modules flush against one another.[10] In a double width case, there will be a gap where the two threaded inserts meet, unless e.g. single 168 HP tiptop Z rails are used.[11]

Oval holes were originally for mixed Analogue Systems and Doepfer systems. The AS holes are 0.2" from the panel edge and the Doepfer holes are 0.3" from the edge. The oval holes were originally used to allow these modules to be placed in the same threaded rows without having the 1/2 HP gap that would otherwise result. These days the oval holes are mostly just centered on the Doepfer spacing.[10]

For front panels up to 10 HP two mounting holes are sufficient, wider than this and four mounting holes are usual. To attach the modules to the mounting rails M3x6 DIN 7985 cross recessed pan head machine screws are used. The mounting hole diameter is 3.2mm (0.13"), centered 3mm from top and bottom edges and 7.45mm from the left edge. The horizontal distance between the mounting holes has to be a multiple of 5.08mm.[3][4][6]

Mounting rails

Eurorack panels mounted on Gie-Tec rails, with sliding nuts. Note the lip along one edge of the rail.

Eurorack panels mounted on Vector rails, with sliding nuts.

Unless attaching the panels directly into the wood of an enclosure; Doepfer aluminium mounting rails from Schroff or Gie-Tech usually have a 1.2mm lip and are fitted with a number of square nuts or a threaded strip with M3 tapped holes, spaced with 5.08mm between centres.[12] Be careful not to get Schroff rails that take M2.5 screws.[13] Vector T-Strut rails do not have a lip and take a M2.5 threaded strip or 4-40 square nuts.[14] Nuts are more fiddly than threaded strip, but the modules can then be butted flush against each other, for example when Analogue Sytem and Doepfer-style modules share the same rack rails.[15]

Blank panels

6061 aluminum alloy, T3 or T6 temper, is easy to come by, can be easily worked. Thickness usually ranges between 1.5 mm (0.62") and 2.5 mm (0.12") but see what is standard for the format, e.g. a thickness of 2 mm (0.08") for 3U. Softer 1100-H aluminium alloy from MetalPhoto and 1.59 mm (0.625") thick, is used for many Euro panels but is usually punched rather than drilled.[18][5]

For small panels it's cheapest to buy Doepfer pre-made blank panels. For wider panels it might be worth getting them done by Frontpanel Express, without labeling and with whatever holes are required. Getting aluminum cut by general online metal suppliers is going to deliver metal that is approximate in size and the edges will need filing down to get it to the correct size.[19]

Front panel labelling options

Front panels parts

PCB dimensions and mounting

These days Eurorack modules tend to mount the PCB parralel to the front panel, held in place by the pots, jacks and switches.[9] Modules with wired front panel components cost more to manufacture than PCB mounted, however these electro-mechanical components have limited lifetimes and while PCB mounted parts can be repaired it's not as easily as wired components. Also PCB mounted components mean the board is designed around specific parts. If any of these parts goes out of production the modules have to be redesigned, with the additional cost of updating the PCBs.[20]

The vertical distance between the mounting holes on Eurorack rails is 122.5mm apart (4.823"). Based on the manufacturer's drawings for the most common rails used in Euro cases, the clear space between pairs of rails is:

112.2mm, 4.415" = Schroff

112.5mm, 4.429" = Gie-Tec and TipTop Z-Rails

115.1mm, 4.531" = Vector

Those don't include the tolerances (slop) of the nut in the rail moving up and down and the screw hole in the front panel. These can cause the rails to be closer or further apart when any given module is tightened in. It's better to try to give a little more clearance and not count on these exact figures.[9]

To fit between the mounting rails the maximum vertical PCB size can be from 108mm (4.25") to 110mm. The width of the PCB needs to be a touch less than that of the front panel, whilst allowing for clearance and taking tolerances into consideration.[3][9][21]

Stacked PCBs

Stacked PCBs can be connected with standard 0.1" single and double row male/female pin headers. These combine to a height of 7/16 inch or 11mm and boards can be mounted to each other with spacers of this length.[22]

Don't use tools you value highly, the headers are made of brittle glass filled epoxy which will damage the edge of any blades used to cut it. To get the single row male headers to length, grip the last pin of the length you want firmly in pliers and snap the rest off. The female headers don't snap easily so first pull the pins out of the body at the point where you want it to snap, then file the ends smooth. Alternately combine smaller lengths to make up the length required. To get them to butt against each other at 0.1" if there is extra plastic on the ends file it down.[22]

Internal connectors

Power connectors

Do not mix terminals and headers made of different metals. With dissimilar metals the contact resistance will go up, causing all sorts of problems.[23]

Caution

Never trust the ribbon cable or the coloured wire. Before connection examine the module, the power distribution bus and the ribbon cable to ensure that matching connections will be made at either end. Even with shrouded headers don't plug the cable in because it fits, always first ensure the correct connections will be made.[24]

Doepfer

Doepfer modules, (the de facto standard)[3] use two row of 8 male pin headers for connecting power and normalisingCV/Gate. The pins are 0.1" (2.54mm) apart and at a 0.1" pitch. The interconnection is done via ribbon cable with 1.27mm (0.05") pitch, and using female sockets, 16-pin to the supply bus and either 16 or 10-pin to the module. The colored wire on the ribbon cable indicates -12V.[25][26][24][27] Pins are numbered from pin 1 with even numbers along one side and the odd numbered ones along the other.[28]

Cwejman

Cwejman uses the same connectors as Doepfer, however +5V is unused. Also on 10 pin connectors the coloured wire indicates Gate and on 16 pin connectors it indicates +12V.[29]

Pin assignments with reference to the front panel for up, on the PCB component side pin 1 is the uppermost on the left:

Power supplies

LC filter to further reduce the amount of output ripple and transients on a switching PS.

A good clean power supply unit (PSU) is the most important part of a modular system. A proper linear power supply and good distribution makes a big difference to the stability and sound quality of the system.[30]

Switch-mode power supplies (SMPS) are smaller, lighter, and much more efficient (give off less heat) than linear power supplies but produce noise, (above the audio range) on their output.[31] About 1% of the output voltage of a switching power is a sawtooth ripple at the switcher frequency. Due to the fast output switching and the parasitic inductance of the output filter capacitor there may also be short voltage spikes at the peaks of the sawtooth. Use low inductance capacitors with short leads to minimize these voltage spikes. Adding a small LC filter to the output can further reduce the ripple and transients to a tenth of their level.[32]

Safety

Mains voltages can kill and capacitors in disconnected power supplies can still deliver quite a jolt. Unless you're qualified to work with mains electricity ready made external transformers are safer.